A known technique relating to a spark plug having a noble metal tip at the forward end of the center electrode is disclosed in Japanese Patent Application Laid-Open (kokai) No. 5-159860. In this technique, the forward end of the center electrode is provided with a dented portion for accommodating a noble metal tip, and a noble metal tip is fit into the dented portion. The noble metal tip is fixed through welding the periphery thereof.
According to the known technique, however, the noble metal tip must have a sufficient length, making use of a noble metal tip having a short length difficult. Thus, difficulty is encountered in enhancing the heat transfer performance of the noble metal tip. Also, since the fusion portion formed through welding has low thermal conductivity, heat transfer of the noble metal tip is problematically impeded.
Also considered relevant prior art is Japanese Patent Application Laid-Open (kokai) No. 5-013145.
The present invention has been conceived to solve, at least partially, the above problems. An advantage of the invention is a technique for enhancing the heat transfer performance of a fusion portion and a noble metal tip.